Better is to make measurements without disconnecting anything. For
example, the green 'power on' wire is above 2 volts disconnected. What
is it when connected - both before power switch is pressed and during a
press. Although this one measurement is not going to report anything
useful, it is how each measurement provides useful facts.

Now what does gray wire do before and in the seconds as power switch
is pressed. Not just 'good' and not just 5 volts. What is the number?
4.87?

And finally what are numbers on one of purple, red, orange, and
yellow wires when and after power switch is pressed?

Is it a motherboard? Maybe. But the point is that in less than 2
minutes, what is failing can be identified without replacing anything.
Furthermore, taking that 5 volt measurement with molex connector
disconnected can look good when the failure still exists. Just another
reason why numbers taken without disconnection anything are so much
more informative.

Once numbers have identified the defective part of the power supply
'system', then a failure might be identified by inspection.
Inspection of an entire motherboard is futile. But once we limit
inspection only to some parts, then inspection why suddenly find that
tiny metal fragment or that slight component bulge.

jim evans wrote:
> I posted this problem in the pc-homebuilt group day before yesterday
> but didn't thing to crosspost to this group, so I'm also posting here.
> Understanding has progressed since my original post, but if you're
> interested in the history go to that group and look for this Subject.
>
> When we got home Sunday my wife's computer was hung in shutdown and
> had been in that state for a day. Holding down the front panel power
> switch would not turn it off. She switched off the rocker switch on
> the power supply. After she switched it back on the box is completely
> dead. No fans, no lights, no sounds, nothing -- a brick.
>
> With the mainboard power connector disconnected, the PS_ON jumpered,
> two hard drives, a floppy drive and a CD drive connected the PS fan
> comes on and all voltages look normal.
>
> With the power connector plugged in to the mainboard, and all molexs
> disconnected, I checked the PS_ON pin. It was 5v, and never changed
> when the power button on the front of the machine was pushed. I know
> this button works, so for some reason closing the power on switch does
> not cause the PSU to get the power on signal/state.
>
> Is this a hopeless motherboard or might there be a fixable cause?